OAI UE: add shared RSRP Table 10.1.6.1-1 mapping helper and adopt it RRC UE

- Add to common/utils/nr/nr_common remove from NR_MAC_UE/nr_ue_procedures.c
- Adopt in asn1_msg.c for MeasurementReport: this solves the following assert:

Assertion (enc_rval.encoded > 0) failed!
In do_nrMeasurementReport_SA() /oai-ran/openair2/RRC/NR/MESSAGES/asn1_msg.c:898
ASN1 message encoding failed (MeasResultServMOList, 18446744073709551615)!

Motivation: unify RSRP-to-index mapping across layers and fix NR RRC MeasurementReport
encoding failures due to out-of-range values by reusing the validated mapping.

Note NR_RSRP-Range.c constraint:
	{ APC_CONSTRAINED,	 7,  7,  0,  127 }	/* (0..127) */

common/utils/nr/nr_common.c

@@ -152,6 +152,17 @@ void reverse_bits_u8(uint8_t const* in, size_t sz, uint8_t* out)
 #endif
 }
 
+/** @brief 3GPP TS 38.133 Table 10.1.6.1-1 mapping from dBm to RSRP index */
+uint8_t get_rsrp_index(int rsrp_dBm)
+{
+  int index = rsrp_dBm + 157;
+  if (rsrp_dBm > -44)
+    index = 113;
+  if (rsrp_dBm < -140)
+    index = 16;
+  return (uint8_t)index;
+}
+
 // Reverse bits implementation based on http://graphics.stanford.edu/~seander/bithacks.html
 uint64_t reverse_bits(uint64_t in, int n_bits)
 {

common/utils/nr/nr_common.h

@@ -186,6 +186,9 @@ typedef struct meas_s {
   val_init_t csi_rsrp_dBm;
 } meas_t;
 
+/** @brief Returns NR RSRP index per 3GPP TS 38.133 Table 10.1.6.1-1 */
+uint8_t get_rsrp_index(int rsrp_dBm);
+
 /**
  * @brief To start a timer
  * @param timer Timer to be started